This invention relates generally to improvements in prosthetic devices, particularly such as hip prostheses and the like. More specifically, this invention relates to an improved prosthesis and related installation tool and method designed to achieve improved tight prosthesis fixation with respect to patient bone, without requiring the use of bone cement for fixation purposes.
Artificial or prosthetic devices for implantation into animals, particularly humans, have been the subject of extensive research and development efforts for many years. Such prosthetic devices have typically comprised one or more implant components formed from a relatively biostable material having selected structural properties and unique shapes to replace all or part of selected bone structures, such as an anatomical joint including, for example, a hip joint. The implant components are installed by surgical access to the subject bone or joint region and by resection of one or more bone surfaces to accommodate direction implant component attachment to the bone.
More specifically, in the context of a hip prosthesis, the hip joint of a patient is accessed surgically to permit removal of the head and neck of the patient's femur to expose the internal medullary canal. A prosthetic component having an artificial femoral head and neck is then implanted by seating an elongated stem of the prosthetic component into the medullary canal. In some procedures, a second prosthetic component is implanted into the patient's acetabulum and cooperates with a typically plastic bearing member to engage the femoral component and thereby form a reconstructed artificial hip joint. In the past, the femoral and/or acetabular prosthetic components have been secured to adjacent patient bone by use of bone cements, such as a methyl methacrylate based cement or the like which interdigitates with the interstices of bone surfaces to achieve mechanical prosthesis fixation.
In recent years, a variety of disadvantages and limitations have been recognized in connection with cemented fixation of prosthetic devices. More particularly, it is now generally recognized that the use of bone cement provides a temporary securement which is relatively weak from a structural standpoint and thereby normally requires significant postoperative patient restrictions to avoid failure of the cemented interface during the patient's lifetime. Failure of the cemented interface is especially undesirable, since the bone cement contributes to localized bone embrittlement and loss of structure such that implantation of a secondary prosthesis can be extremely difficult and sometimes impossible. These problems encountered with cemented prostheses are particularly severe in high load bearing, highly stressed patient joints, such as a hip joint.
In an effort to avoid use of bone cement for prosthesis fixation, a variety of improved prosthetic devices have been developed in recent years for noncemented fixation to patient bone. Many of these improved devices have utilized attachment surfaces of carefully controlled porosity characteristics designed for direct bone attachment by ingrowth or resorption of living cancellous bone or tissue. However, while these bone ingrowth proposals appear to offer significant advantages over prior cemented designs, various problems have still been encountered with respect to insuring positive and stable prosthesis fixation especially at highly loaded and stressed joints, such as the hip. For example, for proper fixation, a relatively tight press-fit relation between the prosthesis and the bone must be obtained and maintained. Any significant movement of the prosthesis relative to the bone during a prolonged postoperative ingrowth period can result in permanent loosening and eventual failure of the prosthesis.
Unfortunately, due to the infinite variation in the size and shape of patient bones and the relatively inexact methods used for bone resection, it is extremely difficult for the surgeon to obtain consistent tight press-fit installation of a prosthesis relative to patient bone. Moreover, although an adequate tight fit of a prosthesis may be apparent during surgery, the surgeon has no effective way to quantify the degree of tight fit, whereby the surgeon cannot know with certainty that a proper prosthesis fit has been achieved. Efforts to overcome these problems have been addressed most often by attempting to implant an oversize prosthesis into an undersize medullary canal or the like. However, this procedure can be extremely difficult and increases the risk of fracturing patient bone during the implantation surgery.
There exists, therefore, a significant need for an improved prosthetic device particularly such as an improved prosthetic hip joint, wherein the prosthetic device is designed for relatively easy implantation into a resected patient bone or the like without significant press-fitting and thereafter expanded in a reliable manner to achieve a relatively strong press-fit interconnection with patient bone. The present invention fulfills these needs and provides further related advantages.